An Ag reflective film has been known to improve the light extraction performance of the Group III nitride semiconductor light-emitting device. However, Ag migration easily occurs. Therefore, Patent Document 1 discloses a structure in which the reflective film is sandwiched between the insulating films formed of SiO2 so as to be electrically insulated, thereby suppressing migration. Moreover, the Ag reflective film has poor adhesion with the SiO2 insulating film. To improve this, an adhesive layer formed of Ti, Ni, Al, W, and Mo having a thickness of 0.3 nm to 3 nm is formed between the reflective film and the insulating film. A conductive film made of a metal such as Al having a larger ionization tendency than Ag is formed on the reflective film, to thereby prevent migration in the reflective film.
Patent Document 2 discloses that an Ag alloy layer is formed, which functions both as an electrode on a p-type layer and a reflective layer of a light-emitting device. Specifically, a p-side electrode has a laminated structure in which a thin film, an Ag alloy layer, a barrier metal layer, and a p-side bonding layer are sequentially formed on a p-GaN layer. The thin film is formed to make a good ohmic contact with the p-GaN layer. The thin film is formed of Pt, Pd, Ni, or Co and has a thickness of 0.5 nm to 5 nm. The Ag alloy layer is formed of Ag alloy including at least one selected from the group consisting of Bi, Nd, Pd, and Mg or Ag alloy including at least one selected from the group consisting of PdCu, BiNd, NdAu, and NdCu. The Ag alloy layer has a thickness of 5 nm to 2000 nm, and functions as a light reflective layer. The barrier metal layer is formed of Ti, Mo, or Pt, or their alloy having a thickness of 10 nm to 200 nm. The barrier metal layer prevents a metal constituting the Ag alloy layer and a metal constituting the p-side bonding layer from diffusing each other. The p-side bonding layer is formed of Au. A technique disclosed in Patent Document 2 is to prevent reduction of reflectance as well as corrosion with a voltage applied even under high temperature and humidity and ion migration in the reflective layer by using the above Ag alloy as a reflective layer.